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J F Whitfield

Publications and source records attributed to J F Whitfield.

At least 181 records · Page 10Linked to original sources
PubMed1980

Steroid biosynthesis by isolated human ovarian follicular cells in vitro.

Cultured thecal preparations from human ovarian follicles obtained from patients during the follicular phase of the menstrual cycle produced large amounts of delta 4-androstenedione and smaller amounts of testosterone and other androgens when stimulated by hCG, (Bu)2cAMP, and prostaglandin E2, but not when stimulated by FSH. Prostaglandin E2 also stimulated thecal cAMP production under the same conditions. By contrast, androgen production by granulosa cells was negligible with or without gonadotropins in the culture medium. Granulosa cells also did not produce 17 beta-estradiol, even when exposed to FSH and hCG, unless supplied with exogenous delta 4-androstenedione. On the other had, thecal, preparations did not produce significant amounts of 17 beta-estradiol even in the presence of FSH, hCG, and relatively large amounts of exogenous delta 4-androstenedione. These observations suggest that delta 4-androstenedione produced by LH or hCG-stimulated thecal cells is the main substrate for the synthesis of 17 beta-estradiol by FSH-stimulated granulosa cells in vivo.

Adult↗
PubMed1980

Stimulation of DNA synthesis in calcium-deprived T51B liver cells by the tumor promoters phenobarbital, saccharin, and 12-O-tetradecanoylphorbol-13-acetate.

Extracellular calcium deprivation arrested the proliferative development of T51B rat liver cells in late G1 or S phases. These arrested cells initiated DNA synthesis within an hr after addition of calcium or a tumor promoter such as phorbol-12,13-didecanoate, phenobarbital, saccharin, or 12-O-tetradecanoylphorbol-13-acetate. Nonpromoting relatives of 12-O-tetradecanoylphorbol-13-acetate such as phorbol, 4-O-methyl-12-O-tetradecanoylphorbol-13-acetate, and 4 alpha-phorbol-12,13-didecanoate were unable significantly to induce the calcium-deprived cells to initiate DNA synthesis. It is suggested that an ability to elicit a prompt DNA-synthetic response from calcium-deprived cells might be a useful in vitro indicator of tumor-promoting potential.

Animals↗
PubMed1979

The regulation of cell proliferation by calcium and cyclic AMP.

Calcium, in partnership with cyclic AMP, controls the proliferation of non-tumorigenic cells in vitro and in vivo. While it does not seem to be involved in the proliferative activation of cells such as hepatocytes (in vivo) or small lymphocytes (in vitro), it does control two later stages of prereplicative (G1) development. It must be one of the very many regulatory and permissive factors affecting early prereplicative development, because severe calcium deprivation reversibly arrests some types of cell early in the G1 phase of their growth-division cycle in vitro. However, calcium more specifically and much more often regulates a later (mid or late G1) stage of prereplicative development. Thus, regardless of its severity or the type of cell, calcium deprivation in vitro or in vivo reversibly stops proliferative development at that part of the G1 phase in which the cellular cyclic AMP content transiently rises and the synthesis of the four deoxyribonucleotides begins. The evidence points to calcium and the cyclic AMP surge being co-generators of the signal committing the cell to DNA synthesis. The evidence is best explained so far by the cyclic AMP surge causing a surge of calcium ions which combine with molecules of the multi-purpose, calcium-dependent, regulator protein calmodulin (CDR) somewhere between the cell surface and the cytosol. The resulting Ca-calmodulin complexes then stimulate many different (and possibly membrane-associated) enzymes such as protein kinases, one of which produces the DNA-synthetic initiator. Calcium has little or no influence on the proliferation of tumor cells. Some possible explanations of this very important loss of control are considered.

Animals↗
PubMed1979

The cyclic AMP-dependent initiation of DNA synthesis by T51B rat liver epithelioid cells.

The brief rise in the cellular cyclic AMP content which occurs late in the prereplicative phases of rat hepatocytes in vivo and T51B rat liver epitheloid cells in vitro seems to be necessary for the initiation of DNA synthesis. Thus, the extracellular calcium-deprivation in T51B rat liver cells in culture which induces a late G-1 block is rapidly reversible (cells surge into S phase within one hour) either by creating a cyclic AMP surge by the addition of calcium or 3-isobutyl-1-methyl xanthine (a cyclic 3',5'-nucleotide phosphodiesterase inhibitor) or by the exogenous addition of low concentrations of cyclic AMP itself (i.e., 10(-8)-10(-5) M). On the other hand, prevention of the calcium-induced cyclic AMP surge by imidazole (a cyclic 3',5'-nucleotide phosphodiesterase activator) blocked the initiation of DNA synthesis by the calcium-deprived T51B cells.

1-Methyl-3-isobutylxanthine↗
PubMed1979

The control of liver regeneration by calcitonin, parathyroid hormone and 1 alpha,25-dihydroxycholecalciferol.

Removal of the thyroid in normocalcemic rats with functional parathyroid transplants was found to reduce the hepatocyte DNA synthetic activity which normally follows partial hepatectomy. This proliferative incapacitation of hepatocytes appeared to be due specifically to a calcitonin deficiency since it was overcome by a single injection of pure synthetic salmon calcitonin shortly after partial hepatectomy. Salmon calcitonin and bovine parathyroid hormone were equally able to reverse the similar proliferative incapacitation of hepatocytes in hypocalcemic rats which had both their parathyroid and thyroid glands removed one day before partial hepatectomy. However, these two hormones (individually or together) could not reverse the proliferative incapacity resulting from a more prolonged (3-day) exposure to the hypocalcemic conditions in thyroparathyroidectomized rats, but the proliferative incapacity could be reversed by simultaneous treatment with the vitamin D3 metabolite, 1 alpha,25-dihydroxycholecalciferol. We suggest that extracellular calcium ions are the actual regulators of this hormonally-controlled hepatocyte proliferative development and that parathyroid hormone and the vitamin D3 metabolite affect proliferation indirectly by determining the extracellular calcium concentration, while calcitonin directly, or indirectly, sensitizes hepatocytes to the action of calcium.

Animals↗
PubMed1978

Polyamine metabolism in regenerating livers from normal and hypocalcemic rats.

There is a marked increase in the concentration of putrescine during the first ten hours following partial hepatectomy in rats. The concentration of spermidine also increases but to a smaller degree. Putrescine levels return to normal between 10 and 24 hours after the operation, whereas the increased spermidine level is maintained. The production of putrescine and spermidine appears to be initiated by the induction of ornithine decarboxylase which shows a single peak of activity at four hours after hepatectomy. The activity of S-adenosylmethionine decarboxylase shows little change following hepatectomy. The changes in polyamine levels and the activities of the enzymes of polyamine metabolism are not affected by thyroparathyroidectomy 72 hours prior to hepatectomy. Thus although these hypocalcemic conditions considerably reduce and delay DNA synthesis and mitosis, the prereplicative changes in polyamine metabolism still occur. These data suggest that the hepatocytes in hypocalcemic animals have become activated and moved to an advanced stage of prereplicative development before being blocked.

Adenosylmethionine Decarboxylase↗
PubMed1978

Age-related and carcinogen-induced alterations of the extracellular growth factor requirements for cell proliferation in vitro.

Cells from thigh muscles of fetal rats proliferate readily in vitro in medium containing homologous adult rat "plasma". As the donor animals mature, these cells become unable to make DNA and proliferate in "plasma" medium, but retain an ability to proliferate in medium containing fetal bovine serum (FBS). This age-related loss of the ability to proliferate in "plasma"-medium is due to an increasing need by the cells for an exogenous prereplicative promoter which is found in FBS and a crude preparation of bovine luteinizing hormone. Adult cells (and possibly fetal cells) also require a "cycle-completion" factor which is found in FBS and adult rat "plasma". The requirements for such external proliferative promoters is completely eliminated by neoplastic transformation in vivo, and neoplastic adult cells isolated from a nickel sulfide-induced mixed rhabdomyo-fibro-sarcoma can make DNA and proliferate in vitro in the complete absence of exogenous growth factors.

Blood↗
PubMed1978

The reduced extracellular calcium requirement for proliferation by neoplastic hepatocytes.

Cells from neonatal rat livers were unable to maintain DNA-synthetic activity in calcium-deficient medium, but neoplastic hepatocytes from Morris hepatomas 5123 tc and 7795 synthesized DNA and proliferated indefinitely in this calcium-deficient medium. The calcium content of fresh hepatoma tissue from which these cultures were derived was as much as 10 times greater than that of normal liver; but this difference could not account for the insensitivity of neoplastic cells to extracellular calcium because it disappeared during subsequent cultivation in vitro.

Animals↗
PubMed1978

Loss of proliferative calcium dependence: simple in vitro indicator of tumorigenicity.

The proliferative activities of three lines of "normal" epithelioid rat liver cells and six tumorigenic liver cell lines in the presence of a wide range of calcium concentrations were measured by a simple colony forming assay. The proliferative activities of the normal cells and, to a lesser extent, of the cells of a marginally tumorigenic line were directly proportional to the extracellular calcium concentration. The proliferative activities of the cells of the strongly tumorigenic lines, on the other hand, were either uninfluenced by or inversely proportional to the extracellular calcium concentration. Thus, the proliferative response to the extracellular calcium concentration is a sensitive indicator of the carcinogenic potential of liver cells.

Animals↗
PubMed1978

Inhibition by colchicine of changes in amino acid transport and initiation of DNA synthesis in regenerating rat liver.

The uptake of amino acids (measured with alpha-aminoisobutyric acid) by hepatocytes stimulated to proliferate by partial hepatectomy followed a biphasic pattern, with an initial peak 8-10 hr after surgery followed by a release of amino acids between 10 and 16 hr and a further increase between 16 and 20 hr after the operation. The second period of increased uptake coincided with the increase in DNA synthesis by the hepatocytes. Colchicine, and other microtubule disrupters administered at the time of partial hepatectomy, abolished the first period of increased amino acid uptake and prevented the cells from initiating DNA synthesis. Pulse-labeling experiments with alpha-aminoisobutyric acid revealed that colchicine did not inhibit amino acid transport per se, but prevented the increased capacity for amino acid transport induced by partial hepatectomy. An injection of colchicine 14 hr after hepatectomy prevented the release of amino acids by the liver and also substantially reduced the initiation of DNA synthesis. The data suggest that the microtubules may play a role in proliferative activation and also in the initiation of DNA synthesis of hepatocytes in vivo and that changes in amino acid transport are linked to these microtubule-requiring processes.

Amino Acids↗
PubMed1978

Calcium requirements for the proliferation of cells infected with a temperature-sensitive mutant of Rous sarcoma virus.

Between 32 degrees and 39 degrees, uninfected normal rat kidney (NRK) cells proliferated minimally, or not at all, in medium containing 0 to 0.01 mM extracellular free calcium. Transformation of NRK cells by wild-type avian sarcoma virus B77 enabled them to proliferate equally rapidly at all temperatures in high (1.25 mM)- or low (0.001 mM-calcium medium. Transformation by the temperature-sensitive LA-23 mutant of Rous sarcoma virus also enabled NRK cells to proliferate in low (0.001 mM)-calcium medium at 32 degrees or 37 degrees. However, the LA-23 NRK cells could not proliferate in low (0.001 mM)-calcium medium at a nonpermissive temperature such as 39 degrees, which prevents expression of other aspects of the transformed phenotype.

Avian Sarcoma Viruses↗
PubMed1977

The control of human WI-38 cell proliferation by extracellular calcium and its elimination by SV-40 virus-induced proliferative transformation.

The proliferative activity of diploid human WI-38 cells in sparse cultures depends on the extracellular concentration of free (or physiologically available) calcium, and cultivation in a medium having a calcium concentration of 0.1 mM or less gradually, but reversibly, arrest their proliferative development in the prereplicative (G1) phase of the cell cycle. Calcium's proliferative control of this cell type is eliminated by proliferative and morphological transformation by the oncogenic SV-40 virus, and the proliferative activity of SV-WI-38 cells in sparse cultures is unaffected by variation of the extracellular free calcium concentration between 0.00 and 1.25 mM.

Calcium↗
PubMed1977

Different extracellular calcium requirements for proliferation of nonneoplastic, preneoplastic, and neoplastic mouse cells.

The DNA-synthetic and proliferative activities of freshly isolated, nontumorigenic C3H mouse skin cells (first passage) were lowest when the extracellular free (or ionic) calcium level was reduced to between 0.05 and 0.1 mM, whereas the extracellular free calcium level in cultures of repeatedly passaged, preneoplastic C3H/10T1/2 and MCA-C3H/10T1/2 type I mouse fetal fibroblasts had to be reduced to 0.01 mM or less before the DNA-synthetic and proliferative activities were minimal. This inhibition of DNA synthesis and cell multiplication by calcium deprivation was rapidly reversed by returning the extracellular calcium level to its normal value. In contrast, the neoplastic fibrosarcoma-forming, MCA-C3H/10T1/2 type III mouse fetal fibroblasts could synthesize DNA and could multiply indefinitely even in the presence of an extremely low concentration of extracellular free calcium. Thus, the extracellular calcium requirement for DNA synthesis and proliferation appears to reflect the tumorigenic potential of the cell.

Calcium↗
PubMed1976

Calcium-dependent stimulation of BALB/c 3T3 mouse cell DNA synthesis by a tumor-promoting phorbol ester (PMA).

During the first six passages after their arrival in this laboratory, BALB/c 3T3 mouse cells did not proliferate in serum containing-medium having an ionic calcium concentration of 0.05 mM or less, but by the ninth passage they had become able to multiply in the presence of these lower calcium levels. In low calcium (e.g., 0.02 mM) medium, passage 1-6, cells in sparse cultures were blocked at the Gl/S boundary of their cycle. These blocked cells could be induced to start making DNA within only one hour either by returning the ionic calcium level to a normal range of values (1.25 mM), or by adding 0.05 mug/ml of PMA (12-O-tetradecanoyl-phorbol-13-acetate). PMA probably acted by sensitizing the blocked cells to calcium rather than replacing the ion, because it was ineffective in ionic calcium-free medium. Finally, PMA did not by itself induce proliferation of cells (regardless of the number of passages) which had been proliferatively inactivated by density-dependent factors in confluent cultures. However, PMA did promote DNA synthesis by these cells during their brief transition to the "cycling" state caused by exposure to fresh serum-containing medium.

Calcium↗